Polymerization method and product

ABSTRACT

Methods of preparing a polyaniline homopolymer or copolymer comprising at least one carboxylic acid group, and homopolymers or copolymers arising therefrom, the methods comprising: preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group (eg. 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoic acid) in a solvent selected from aqueous methanesulfonic acid or aqueous ammonia and optionally one or more additional polyaniline precursors (such as aniline); and oxidatively polymerising the polyaniline precursor or precursors.

TECHNICAL FIELD

The invention relates to processes for preparing polymers that includeaminobenzoic acid monomers, and to copolymers and homopolymers preparedby those processes.

BACKGROUND ART

Polymers of aniline and its derivatives are useful as antimicrobialagents and have good antistatic and free radical scavenging properties.These properties make them useful for the manufacture of antimicrobial,antistatic and antioxidant objects, and suitable for use in, forexample, the health, food, packaging, water, paint, wood, textile,poultry, glass, paper, rubber, ceramic, seafood, sports, plastic andagricultural industries.

Adding substituents to polyaniline (PANI) is one way in which thevarious properties of the polymer can be improved. However, thesynthesis of substituted PANIs is not always a straightforward matter.Any substituent introduced to the aniline building block needs to becompatible with the reagents used, which is not always possible underthe traditionally robust oxidative polymerisation conditions used toform PANIs.

Carboxylated PANIs are one type of PANT derivative of particularinterest due to their good antibacterial properties. Carboxylated PANIscan either be homopolymers, which could also be described as apoly(aminobenzoic acid) (poly ABAs) or copolymers, which could beconsidered as a PANT backbone bearing carboxylic acid groups on some ofthe aromatic rings. The probable structure of poly(2-aminobenzoic acid)and poly(3-aminobenzoic acid) (top) and the probable structure ofcopolymers of aniline and 2-aminobenzoic acid or 3-aminobenzoic acid(bottom), where X and Y are the numbers of repeat units are shown below.

However, producing PANI homopolymers and copolymers from aminobenzoicacid (ABA) monomers in good yield and purity is not a simple procedure.There are significant problems with the solubilities of ABAs. ABAs tendto be solids, unlike aniline itself or many substituted anilines (alkylanilines like toluidine, alkoxy anilines like anisidine etc) which canbe used directly in their liquid form. This low solubility impacts uponthe cost of synthesis and the quality of the resultant polymers.

There thus exists a need to produce poly-ABAs (carboxylated PANis) inhigh yield and in a cost effective manner, with high conversion ofmonomer units, short production time and high molecular weights.

It is an object of the present invention to overcome or ameliorate atleast one of the disadvantages of the prior art, or to provide a usefulalternative.

SUMMARY

In a broad aspect, the invention provides a method of preparing apolyaniline homopolymer or copolymer comprising at least one carboxylicacid group; the method comprising:

preparing a solution of a polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group in a solventselected from aqueous methanesulfonic acid or aqueous ammonia andoptionally one or more additional polyaniline precursors; andoxidatively polymerising the polyaniline precursor or precursors.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise”, “comprising”, and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”.

In one aspect, the invention provides a method of preparing apolyaniline homopolymer comprising carboxylic acid groups; the methodcomprising:

preparing a solution of a polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group in aqueousmethanesulfonic acid; andoxidatively polymerising the polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group.

In one aspect, the invention provides a method of preparing apolyaniline homopolymer comprising carboxylic acid groups; the methodcomprising:

preparing a solution of a polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group in aqueousammonia; andoxidatively polymerising the polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group.

The polyaniline precursor having at least one aromatic amine group andat least one carboxylic acid group may be any aromatic ring bearing —NH₂and —COOH moieties in any position, with or without other substituents.In certain preferred embodiments, the substance being polymerised isselected from 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoicacid.

Monomers other than amino benzoic acids can be used, for example anilineor pyrrole, or derivatives thereof may be used.

In one aspect, the invention provides a method of preparing apolyaniline copolymer comprising at least one carboxylic acid group; themethod comprising:

preparing a solution of a polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group in aqueousmethanesulfonic acid and one or more additional polyaniline precursors;andoxidatively polymerising the polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group and the oneor more additional polyaniline precursors.

In one aspect, the invention provides a method of preparing apolyaniline copolymer comprising at least one carboxylic acid group; themethod comprising:

preparing a solution of a polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group in aqueousammonia and one or more additional polyaniline precursors; andoxidatively polymerising the polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group and the oneor more additional polyaniline precursors.

The polyaniline precursor having at least one aromatic amine group andat least one carboxylic acid group may be any aromatic ring bearing —NH₂and —COOH moieties in any position, with or without other substituents.In certain preferred embodiments, the substance being polymerised isselected from 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoicacid. The one or more additional polyaniline precursors may be any aminosubstituted aromatic ring, which is in some cases preferably comprisesaniline.

A possible structure of poly(4-aminobenzoic acid) is shown below.

Monomers other than aminobenzoic acids can be used, for example anilineand other derivatives thereof or pyrrole and derivatives thereof may beused.

The most preferred copolymers are those formed from mixtures of anilineand 2-aminobenzoic acid, aniline and 3-aminobenzoic acid or aniline and4-aminobenzoic acid. The possible structure of copolymers of aniline and4-aminobenzoic Acid is shown below. Y and Z are the numbers of repeatunits.

The ratio of the polyaniline precursor having at least one aromaticamine group and at least one carboxylic acid group: the one or moreadditional polyaniline precursors is from 99:1 to 1:99. Alternatively,ratios in the range 72:25 to 25:75 may be used.

If aqueous methane sulfonic acid is used, it is preferably in aconcentration of 0.1 to 10 M in water. It is generally preferred if theratio of concentration of ABA to methanesulfonic acid is from 2:1 to1:2. For example, it is preferred to use a solution of methanesulfonicacid of around 1 M and an ABA concentration of around 0.5 M.

The polyaniline precursor having at least one aromatic amine group andat least one carboxylic acid group is preferably dissolved in theaqueous methane sulfonic acid and oxidising agent is added. If acopolymer is desired, additional polyaniline precursors may be added ina suitable compatible solvent, which may include water or aqueousmethane sulfonic acid.

If ammonia is used, the polyaniline precursor having at least onearomatic amine group and at least one carboxylic acid group is suspendedin water and ammonia is added to dissolve it. The amount andconcentration required can be readily determined. Typically, commercialstrength ammonia is added to a suspension of the ABA in water until themonomer is dissolved. The pH is readily maintained at around neutral toslightly alkaline pHs, for example around pH 7-8.

The reaction of aminobenzoic acid and/or aniline to synthesize thehomopolymer or copolymer is carried out in an acidic or near neutralmedium in the presence of an oxidizing agent. Any suitable oxidizingagent may be used. Suitable oxidizing agents include, although are notlimited to ammonium persulphate, potassium ferricyanide, potassiumiodate, hydrogen peroxide, cerium (IV) sulphate, potassium dichromateand sodium vanadate. For neutral/alkaline based reaction, preferably theoxidizing agent is ammonium persulphate or hydrogen peroxide.

The methods of the present invention will also usually further includethe step of collecting the precipitated poly aminobenzoic acidhomopolymer or copolymer by filtration.

DESCRIPTION

Aminobenzoic acids have low solubility in water and in common acids usedto carry out oxidative polymerization. For example, 3-ABA has onlyaround 5 wt % solubility in 1 M HCl, which is typical for ABAsgenerally. Even if the aminobenzoic acids can be dissolved to someextent, it is difficult to get them into solution at sufficiently highconcentrations to achieve good yields of the resultant polyanilinepolymer or copolymer. The present inventors have developed solventsystems based around methanesulfonic acid or ammonia that enable themonomer to be dissolved in MSA or ammonia at high concentration (15% byweight or higher)

The methods of the present invention enable the practical large scaleproduction of PANIs, particularly those starting from amino benzoic acidderivatives, at room temperature. Because of the good solubility of thestarting monomers, the reaction yield and starting monomer consumptionis high and the reaction time is reduced, resulting in a less wastefuland more economic synthesis. Moreover, the products of the presentinvention have been found to have high molecular weight and, wherecopolymers are concerned, high incorporation of n-ABA in the resultantcopolymer is observed.

COMPARATIVE EXAMPLES

Oxidative polymerisation of 3-amino benzoic acid to the correspondingpolycarboxylated PANI was carried out under standard conditions using 1MHCl as monomer solvent and APS as oxidant.

From 150 ml 1 M HCl solution containing 2.2 g (16 mmol) 3-ABA, 0.0154 gpolymer was obtained (0.7% yield*) when the reaction was performed at10° C. for 7 days

From 200 g 1 M HCl solution containing 10 g n-ABA monomer, 1 g polymerwas obtained (10% yield*), when the reaction was performed at roomtemperature for 48 h

*Yield:=100×[mass of the polymer]/[mass of the (co)monomer(s)]

INVENTIVE EXAMPLES Methane Sulfonic Acid as Solvent

Poly(n-amino benzoic acid) homopolymers, where n=2, 3 or 4 (P(n-ABA))and poly(n-amino benzoic acid-co-aniline) copolymers (P(n-ABA-co-Ani))were synthesised in 1 M methane sulfonic acid (MSA) at 25° C. (ambienttemperature), with ammonium persulfate (APS) as the oxidizing agent. Themonomer(s) concentration and the mole ratio of monomer(s) to APS werekept constant at 0.5 M and 1:1.25 respectively. The mole ratio ofn-aminobenzoic acid (n-ABA) to aniline (Ani) in the comonomer mixtureswas varied from 99:1 to 1:99, or more usually 75:25 to 25:75.

The maximum concentration of n-aminobenzoic acid (n-ABA) in 1 M MSA isabout 15%, which may be higher in more concentrated MSA.

Homopolymers

Homopolymers of the present invention can be designated as follows:

HpMn: Hp=Homopolymer, M=methane sulfonic acid (MSA), n=position of —COOHfunctional group (4 or 3 or 2) in n-ABA precursor.HpAn: Hp=Homopolymer, A=ammonia, n=position of —COOH functional group (4or 3 or 2) in n-ABA precursor.

Synthesis of PANI homopolymers of aminobenzoic acids P(n-ABA): 13.86 gof 4-ABA was dissolved in 100 mL of 1 M MSA. 28.52 g of APS wasdissolved in 100 mL of water and added dropwise to the monomer solutionwith constant stirring. Polymerisation was continued with stirring for24 h. The polymeric product that precipitated from the solution wascollected by filtration, washed thoroughly with distilled water then(vacuum) dried at 50° C. From this process 7.2 g polymer HpM4 wasobtained (52% yield).

The yield can be seen to be significantly better than that obtained fromthe use of HCl as solvent.

The use of 3-ABA and 2-ABA in an identical manner resulted in thesynthesis of a homopolymer of 3-aminobenzoic HpM3 and a homopolymer of2-aminobenzoic acid HpM2 respectively.

Table 1 shows the properties of HpMn homopolymers synthesised using MSAas solvent. The yields are significantly better than using traditionalsolvents, such as HCl.

TABLE 1 Antimicrobial property Free radical (Minimum inhibitoryscavenging concentration) % (μmol DPPH Yield Mol wt. Gram +ve Gram −vescavenged/mg Conductivity Material Monomer Colour (%) (g/mol) (S.aureus) (E. coli) of sample) % (S/cm) HpM4 4ABA Dark 52 19826 0.5 1 64<10⁻⁵ brown HpM3 3ABA Dark 18 12947 1 >2% 60 <10⁻³ brown HpM2 2ABA Dark30 22200 0.25 1 61 <10⁻⁵ brown

Copolymers

Copolymers of the present invention can be designated as follows:

CpMnYZ: Cp=Copolymer, M=methane sulfonic acid (MSA), n=position of —COOHfunctional group (4 or 3 or 2) in n-ABA precursor, YZ ratio Y:Z ofn-ABA:aniline in feed.CpAnYZ: Cp=Copolymer, A=ammonia, n=position of —COOH functional group (4or 3 or 2) in n-ABA precursor, YZ ratio Y:Z of n-ABA:aniline in feed.

Synthesis of copolymers of aminobenzoic acids and anilineP(n-ABA-co-Ani): For a typical synthesis of P(n-ABA-co-Ani) (startingfrom a solution with equimolar proportions of comonomers, for example),6.94 g of n-ABA was dissolved in 100 mL of 1 M MSA. 4.66 g aniline wasadded to this solution and stirred for 15 mins. 28.52 g of APS wasdissolved in 100 mL of water and added dropwise to the solution of themonomers with constant stirring. Polymerisation was continued withstirring for 24 h. The polymer product that precipitated from thesolution was collected by filtration, washed thoroughly with distilledwater then (vacuum) dried at 50° C.

Oxidative synthesis of copolymer CpM411: 6.94 g of 4-ABA was dissolvedin 100 mL of 1 M MSA. 4.66 g aniline was added to this solution andstirred for 15 mins. 28.52 g of APS was dissolved in 100 mL of water andadded dropwise to the solution of the monomers with constant stirring.Polymerisation was continued with stirring for 24 h. The polymer productthat precipitated from the solution was collected by filtration, washedthoroughly with distilled water then (vacuum) dried at 50° C. From thisprocess 11.6 g copolymer (CpM411) was obtained (100% yield).

Under similar conditions, copolymers of 4-ABA and aniline, copolymers of3-ABA and aniline, copolymers of 2-ABA and aniline at various monomerfeed ratio (from 99:1 to 1:99) can be synthesized.

Table 2 shows the properties of copolymers (CpMnYZ) synthesised inacidic medium.

TABLE 2 Free radical Antimicrobial property scavenging (Minimuminhibitory (micromoles concentration) % of DPPH Monomer ratio Yield Gram+ve Gram −ve scavenged/mg Conductivity Material (n-ABA:Aniline) Colour(%) (S. aureus) (E. coli) of sample) % (S/cm) CpM431 4ABA:Aniline (3:1)Dark 78 0.25  2 57 <10⁻⁵ brown CpM411 4ABA:Aniline (1:1) Dark 100 0.5 >259 0.002 brown CpM413 4ABA:Aniline (1:3) Dark 112 0.5 >2 60 1 greenCpM331 3ABA:Aniline (3:1) Dark 85 0.5  2 57 <10⁻⁵ brown CpM3113ABA:Aniline (1:1) Dark 101 2 >2 54 0.002 brown CpM313 3ABA:Aniline(1:3) Dark 114 >2 >2 46 0.6 green CpM231 2ABA:Aniline (3:1) Dark 78 0.5 2 54 <10⁻⁵ brown CpM211 2ABA:Aniline (1:1) Dark 81 0.5 >2 47 0.04 brownCpM213 2ABA:Aniline (1:3) Dark 121 0.5 >2 54 2 green

Ammonia as Solvent Homopolymers

Synthesis of HpA4 in non-acidic medium (by neutralizing monomer withammonia): 13.86 g monomer (4-ABA) was dissolved in 100 mL water byneutralizing with 7.5 mL of 28% ammonia. 28.52 g of APS was dissolved in92.5 mL of water and added dropwise to the monomer solution withconstant stirring. Polymerisation was continued with stirring for 24 h.The polymeric product that precipitated out from the solution wascollected by filtration, washed thoroughly with distilled water then(vacuum) dried at 50° C. From this process 11.37 g polymer HpA4 wasobtained (82% yield).

Again, the yield can be seen to be significantly better than thatobtained from the use of HCl as solvent. Under the same conditions HpA3and HpA2 can be synthesized in non-acidic medium (by neutralizingmonomer with ammonia.)

A possible reaction scheme for synthesis of poly(4-aminobenzoic acid) isshown below.

Table 3 shows the properties of HpAn homopolymers synthesised bypre-neutralization with ammonia

TABLE 3 Free radical Antimicrobial property scavenging (Minimuminhibitory (μmol concentration % DPPH Yield Mol wt Gram +ve Gram −vescavenged/mg Conductivity Material Monomer Colour (%) (g/mol) (S.aureus) (E. coli) of sample) % (S/cm) HPA4 4ABA Dark 82 18362 0.125 >2 55 <10⁻³ brown HPA3 3ABA Dark 82 62847 1 2 61 <10⁻⁵ brown HPA2 2ABA Dark71 44645 0.5 1 56 <10⁻⁵ brown

Copolymers

Oxidative synthesis of copolymer CpA411: 6.94 g monomer (4-ABA) wasdissolved in 100 mL water by neutralizing with 4 mL of 28% ammonia. 4.66g aniline was added to this solution and stirred for 15 mins. 28.52 g ofAPS was dissolved in 96 mL of water and added dropwise to the monomersolution with constant stirring. Polymerisation was continued withstirring for 24 h. The polymeric product that precipitated out from thesolution was collected by filtration, washed thoroughly with distilledwater then (vacuum) dried at 50° C. From this process 10.2 g copolymer(CpA411) was obtained (88% yield).

Under similar conditions, copolymers of (4-ABA) and aniline, (3-ABA) andaniline, and (2-ABA) and aniline at various monomer feed ratio (can befrom 99:1 to 1:99) can be synthesized in acidic medium.

Table 4 shows a property chart of copolymers (CpAnYZ) synthesised bypre-neutralization of monomer n-ABA with ammonia

TABLE 4 Free radical Antimicrobial property scavenging (Minimuminhibitory (micromoles concentration) % of DPPH Monomer ratio Yield Gram+ve Gram −ve scavenged/mg Conductivity Material (n-ABA:Aniline) Colour(%) (S aureus) (E. coli) of sample) % (S/cm) CpA431 4ABA:Aniline (3:1)Dark 83 0.06% >2% 60 <10⁻⁵ brown CpA411 4ABA:Aniline (1:1) Dark 880.13% >2% 58 <10⁻⁵ brown CpA413 4ABA:Aniline (1:3) Dark 90 0.25% >2% 550.0003  green CpA331 3ABA:Aniline (3:1) Dark 83 0.125 >2  58 <10⁻⁵ brownCpA311 3ABA:Aniline (1:1) Dark 87 0.125 >2  61 <10⁻⁵ brown CpA3133ABA:Aniline (1:3) Dark 85 0.25 >2  55 0.00005 green CpA231 2ABA:Aniline(3:1) Dark 72 0.125 1  53 <10⁻⁵ brown CpA211 2ABA:Aniline (1:1) Dark 910.125 2  52 <10⁻⁵ brown CpA213 2ABA:Aniline (1:3) Dark 93 0.25 >2  56<10⁻⁵ green

The claims defining the invention are as follows:
 1. A polyanilinehomopolymer or copolymer prepared by the method comprising: preparing anacidic or near neutral (pH 7-8) solution of 15% by weight or higher of afirst polyaniline precursor having at least one aromatic amine group andat least one carboxylic acid group in a solvent selected from the groupconsisting of aqueous methanesulfonic acid and aqueous ammonia; whereinsaid solution optionally includes one or more additional polyanilineprecursors; oxidatively polymerizing said solution and additionalpolyaniline precursors if present; finally collecting precipitatedpolyaniline by filtration.
 2. A polyaniline homopolymer as in claim 1wherein the polyaniline precursor is selected from 2-aminobenzoic acid,3-aminobenzoic acid, or 4-aminobenozic acid.
 3. A polyaniline randomcopolymer as in claim 1 wherein the first polyaniline precursor isselected from either 2-aminobenzoic acid, 3-aminobenzoic acid, or4-aminobenzoic acid and the second polyaniline precursor is aniline. 4.A polyaniline random copolymer as in claim 3 composed of 3ABA andaniline monomers.
 5. A polyaniline random copolymer as in claim 3wherein the monomer ratio of 3ABA and aniline monomers is 1:1.
 6. Apolyaniline random copolymer as in claim 3 wherein the monomer ratio of3ABA acid to aniline is from 3:1 to 1:3.
 7. A polyaniline randomcopolymer as in claim 3 composed of 2ABA and aniline monomers
 8. Apolyaniline random copolymer as in claim 3 wherein the monomer ratio of2ABA acid to aniline is 1:1.
 9. A polyaniline random copolymer as inclaim 3 wherein the monomer ratio of 2ABA and aniline monomers is from3:1 to 1:3
 10. A polyaniline random copolymer as in claim 3 composed of4ABA and aniline monomers
 11. A polyaniline random copolymer as in claim3 wherein the monomer ratio of 4ABA acid to aniline is 1:1.
 12. Apolyaniline random copolymer as in claim 3 wherein the monomer ratio of4ABA and aniline monomers is from 3:1 to 1:3.